Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device and its manufacturing method are presented. The manufacturing method entails: providing a semiconductor substrate, wherein the semiconductor substrate comprises a first region and a second region that are mutually exclusive from one another, with a first oxide layer on the first and the second regions; conducting a nitriding process on the semiconductor substrate to form a nitride barrier layer on the first oxide layer on the first and the second regions; removing the first oxide layer on the second region; and conducting an oxidation process to form a second oxide layer on the second region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/821,349 filed on Nov. 22, 2017, which claims priority toChinese Patent Application No. 201611048954.5 filed on Nov. 24, 2016,and all the benefits accruing therefrom under 35 U.S.C. § 119, thecontents of the prior applications being herein incorporated byreference.

BACKGROUND (a) Field of the Invention

This inventive concept relates to semiconductor technology, morespecifically, a semiconductor device and its manufacturing method.

(b) Description of the Related Art

NOR flash memory has been widely used in embedded systems to read andwrite programs. Compared to NAND flash memory, NOR flash memory providesbetter performance on data reading and writing, and supports in-chipdata processing with eXecute-In-Place (XIP).

However, as the density of memory units in a NOR flash memory increases,the thickness of a tunnel oxide layer in the NOR flash memory may goout-of-spec in some regions, which in turn increases a threshold voltageof the NOR flash memory in those regions.

SUMMARY

This inventive concept presents a semiconductor manufacturing methodthat can prevent the thickness of an oxide layer from gettingout-of-spec in designated areas.

This semiconductor manufacturing method comprises:

providing a semiconductor substrate, wherein the semiconductor substratecomprises a first region and a second region that are mutually exclusivefrom one another, with a first oxide layer on the first and the secondregions;

conducting a nitriding process to form a nitride barrier layer on thefirst oxide layer on the first and the second regions;

removing the nitride barrier layer and the first oxide layer on thesecond region; and

conducting an oxidation process to form a second oxide layer on thesecond region.

Additionally, in the aforementioned method, the semiconductor substratemay further comprise:

a third region different from the first region and the second region;and

a third oxide layer on the third region, wherein the thickness of thethird oxide layer is larger than the thickness of the second oxidelayer,

and wherein the nitriding process also forms a nitride barrier layer onthe third oxide layer.

Additionally, in the aforementioned method, providing a semiconductorsubstrate may comprise:

providing the semiconductor substrate comprising the first region, thesecond region and the third region that are mutually exclusive from oneanother;

forming the third oxide layer on the first region, the second region andthe third region;

removing the third oxide layer on the first and the second regions; and

forming the first oxide layer on the first and the second regions.

Additionally, in the aforementioned method, conducting a nitridingprocess may comprise:

conducting a Decouple Plasma Nitriding (DPN) process; and

conducting a Post-Nitriding Annealing (PNA) process.

Additionally, in the aforementioned method, removing the nitride barrierlayer on the second region and the first oxide layer on the secondregion may comprise:

forming a photomask layer on the semiconductor substrate;

patternizing the photomask layer to expose the nitride barrier layer onthe second region and the first oxide layer on the second region; and

removing the nitride barrier layer on the second region and the firstoxide layer on the second region.

Additionally, in the aforementioned method, the photomask layer maycomprise:

a protection layer to prevent photoresist poisoning; and

a photoresist on the protection layer,

and the aforementioned method may further comprise:

removing the remaining photomask layer; or

removing the photoresist of the remaining photomask layer whileretaining the protection layer of the remaining photomask layer.

Additionally, in the aforementioned method, the protection layer may bemade of silicon oxide, amorphous carbon, or poly-silicon.

Additionally, in the aforementioned method, a nitrogen dose in thenitriding process may be from 5×10¹⁵ atoms/cm² to 2×10¹⁶ atoms/cm².

Additionally, in the aforementioned method, the nitride barrier layermay be made of silicon oxynitride (SiON).

Additionally, in the aforementioned method, the thickness of the nitridebarrier layer may be from 3 Angstrom to 50 Angstrom.

Additionally, in the aforementioned method, the first oxide layer may bea tunnel oxide layer for a flash memory device.

Additionally, the aforementioned method may further comprise forming afloating gate and a control gate on the nitride barrier layer on thefirst region.

This inventive concept further presents a semiconductor device,comprising:

a semiconductor substrate, comprising a first region and a second regionthat are mutually exclusive from one another;

a first oxide layer on the first region;

a nitride barrier layer on the first oxide layer; and

a second oxide layer on the second region.

Additionally, in the aforementioned device, the semiconductor substratemay further comprise:

a third region that is different from the first region and the secondregion,

and the aforementioned device may further comprise a third oxide layeron the third region, wherein the nitride barrier layer covers the thirdoxide layer, and the thickness of the third oxide layer is larger thanthe thickness of the second oxide layer.

Additionally, the aforementioned device may further comprise aprotection layer on the nitride barrier layer to prevent photoresistpoisoning.

Additionally, in the aforementioned device, the protection layer may bemade of silicon oxide, amorphous carbon, or poly-silicon.

Additionally, in the aforementioned device, the nitride barrier layermay be made of silicon oxynitride (SiON).

Additionally, in the aforementioned device, the thickness of the nitridebarrier layer may be from 3 Angstrom to 50 Angstrom.

Additionally, in the aforementioned device, the first oxide layer may bea tunnel oxide layer for a flash memory device.

Additionally, the aforementioned device may further comprise a floatinggate and a control gate on the nitride barrier layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate some embodiments of this inventive concept andwill be used to describe this inventive concept along with thespecification.

FIG. 1 shows a flowchart illustrating a semiconductor devicemanufacturing method in accordance with one or more embodiments of thisinventive concept.

FIGS. 2, 3, 4, and 5 show schematic sectional views illustratingdifferent stages of a semiconductor device manufacturing method inaccordance with one or more embodiments of this inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example embodiments of the inventive concept are described withreference to the accompanying drawings. As those skilled in the artwould realize, the described embodiments may be modified in various wayswithout departing from the spirit or scope of the inventive concept.Embodiments may be practiced without some or all of these specifieddetails. Well known process steps and/or structures may not be describedin detail, in the interest of clarity.

The drawings and descriptions are illustrative and not restrictive. Likereference numerals may designate like (e.g., analogous or identical)elements in the specification. To the extent possible, any repetitivedescription will be minimized.

Relative sizes and thicknesses of elements shown in the drawings arechosen to facilitate description and understanding, without limiting theinventive concept. In the drawings, the thicknesses of some layers,films, panels, regions, etc., may be exaggerated for clarity.

Embodiments in the figures may represent idealized illustrations.Variations from the shapes illustrated may be possible, for example dueto manufacturing techniques and/or tolerances. Thus, the exampleembodiments shall not be construed as limited to the shapes or regionsillustrated herein but are to include deviations in the shapes. Forexample, an etched region illustrated as a rectangle may have rounded orcurved features. The shapes and regions illustrated in the figures areillustrative and shall not limit the scope of the embodiments.

Although the terms “first,” “second,” etc. may be used herein todescribe various elements, these elements shall not be limited by theseterms. These terms may be used to distinguish one element from anotherelement. Thus, a first element discussed below may be termed a secondelement without departing from the teachings of the present inventiveconcept. The description of an element as a “first” element may notrequire or imply the presence of a second element or other elements. Theterms “first,” “second,” etc. may also be used herein to differentiatedifferent categories or sets of elements. For conciseness, the terms“first,” “second,” etc. may represent “first-category (or first-set),”“second-category (or second-set),” etc., respectively.

If a first element (such as a layer, film, region, or substrate) isreferred to as being “on,” “neighboring,” “connected to,” or “coupledwith” a second element, then the first element can be directly on,directly neighboring, directly connected to or directly coupled with thesecond element, or an intervening element may also be present betweenthe first element and the second element. If a first element is referredto as being “directly on,” “directly neighboring,” “directly connectedto,” or “directly coupled with” a second element, then no intendedintervening element (except environmental elements such as air) may alsobe present between the first element and the second element.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element or feature's spatial relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms may encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientation), and the spatially relative descriptorsused herein shall be interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to limit the inventive concept. As usedherein, singular forms, “a,” “an,” and “the” may indicate plural formsas well, unless the context clearly indicates otherwise. The terms“includes” and/or “including,” when used in this specification, mayspecify the presence of stated features, integers, steps, operations,elements, and/or components, but may not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups.

Unless otherwise defined, terms (including technical and scientificterms) used herein have the same meanings as what is commonly understoodby one of ordinary skill in the art related to this field. Terms, suchas those defined in commonly used dictionaries, shall be interpreted ashaving meanings that are consistent with their meanings in the contextof the relevant art and shall not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

The term “connect” may mean “electrically connect.” The term “insulate”may mean “electrically insulate.”

Unless explicitly described to the contrary, the word “comprise” andvariations such as “comprises,” “comprising,” “include,” or “including”may imply the inclusion of stated elements but not the exclusion ofother elements.

Various embodiments, including methods and techniques, are described inthis disclosure. Embodiments of the inventive concept may also cover anarticle of manufacture that includes a non-transitory computer readablemedium on which computer-readable instructions for carrying outembodiments of the inventive technique are stored. The computer readablemedium may include, for example, semiconductor, magnetic, opto-magnetic,optical, or other forms of computer readable medium for storing computerreadable code. Further, the inventive concept may also cover apparatusesfor practicing embodiments of the inventive concept. Such apparatus mayinclude circuits, dedicated and/or programmable, to carry out operationspertaining to embodiments of the inventive concept. Examples of suchapparatus include a general purpose computer and/or a dedicatedcomputing device when appropriately programmed and may include acombination of a computer/computing device and dedicated/programmablehardware circuits (such as electrical, mechanical, and/or opticalcircuits) adapted for the various operations pertaining to embodimentsof the inventive concept.

In the manufacture of semiconductor devices, different devices, such asHigh Voltage device, Low Voltage device, and flash memory, may need tobe manufactured simultaneously on a substrate. Therefore, after a tunneloxide layer for a flash memory is formed on a substrate, additionalprocesses may be needed to form oxide layers for other devices, theseadditional processes may incidentally thicken the tunnel oxide layer forthe flash memory and thus increase its threshold voltage. Asemiconductor device manufacturing method remedying this situation isdescribed below.

FIG. 1 shows a flowchart illustrating a semiconductor devicemanufacturing method in accordance with one or more embodiments of thisinventive concept. FIGS. 2, 3, 4, and 5 show schematic sectional viewsillustrating different stages of a semiconductor device manufacturingmethod in accordance with one or more embodiments of this inventiveconcept. Referring to these figures, a semiconductor devicemanufacturing method in accordance with one or more embodiments of thisinventive concept will be described below.

In step 102, a semiconductor substrate 201 is provided. Referring toFIG. 2, the semiconductor substrate 201 may comprise a first region 211and a second region 221 that are mutually exclusive from one another,with a first oxide layer 203 is formed on the first region 211 and thesecond region 221. The first region 211 and the second region 221 may beseparated by a separation structure 202, which can be a Shallow TrenchIsolation (STI) structure.

In one embodiment, the semiconductor substrate 201 may further comprisea third region 231 different from the first region 211 and the secondregion 221, and a third oxide layer 204 on the third region 231. Here,the first region 211 is a region for a flash memory device, the secondregion 221 and the third region 231 are regions for a Low Voltage deviceand a High Voltage device, respectively. It is understood that low/highvoltage of a device refers to its threshold voltage, with the thresholdvoltage of a Low Voltage device lower than the threshold voltage of aHigh Voltage device. In one embodiment, the first oxide layer 203 is atunnel oxide layer for a flash memory device such as a NOR flash memory,and the third oxide layer 204 is an oxide layer for a High Voltagedevice.

In one embodiment, the structure of FIG. 2 can be formed by thefollowing process. First, the semiconductor substrate 201 is provided,wherein the semiconductor substrate 201 comprises the first region 211,the second region 221, and the third region 231 that are mutuallyexclusive of one another. The third oxide layer 204 is formed on thefirst region 211, the second region 221, and the third region 231through an oxidation process, then the third oxide layer 204 on thefirst region 211 and the second region 221 is removed while the thirdoxide layer 204 on the third region 231 remains. Then a first oxidelayer 203 is formed on the first region 211 and the second region 221through an oxidation process, resulting in the structure of FIG. 2.

In step 104, a nitride barrier layer 301 is formed on the first oxidelayer 203 on the first region 211 and the second region 221 through anitriding process, as shown in FIG. 3. The nitride barrier layer 301 maybe made of silicon oxynitride (SiON). If the semiconductor substrate 201comprises the third region 231, the nitride barrier layer 301 is alsoformed on the third oxide layer 204 on the third region 231.

In one embodiment, the nitriding process comprises two steps: conductinga Decouple Plasma Nitriding (DPN) process; and conducting aPost-Nitriding Annealing (PNA) process. In one embodiment, a nitrogendose in the nitriding process can be from 5×10¹⁵ atoms/cm² to 2×10¹⁶atoms/cm². For example, it can be 7×10¹⁵ atoms/cm², 9×10¹⁵ atoms/cm², or1×10¹⁶ atoms/cm². The nitride barrier layer 301 may be formed on thefirst oxide layer 203 through the DPN and PNA processes. Optimally, thethickness of the nitride barrier layer 301 may be from 3 Angstrom to 50Angstrom. For example, it can be 10 Angstrom, 30 Angstrom, or 40Angstrom.

In step 106, after the nitriding process, the nitride barrier layer 301on the second region 221 and the first oxide layer 203 on the secondregion 221 are both removed, as shown in FIG. 4.

In one embodiment, the nitride barrier layer 301 on the second region221 and the first oxide layer 203 on the second region 221 may beremoved by the following process. First, after the nitriding process, aphotomask layer is formed on the semiconductor substrate 201. In oneembodiment, the photomask layer may comprise a photoresist. In anotherembodiment, the photomask layer may comprise a protection layer toprevent photoresist poisoning and a photoresist on the protection layer.The protection layer protects the photoresist from contacting thenitride barrier layer 301 to cause photoresist poisoning. Optimally, theprotection layer may be made of silicon oxide, amorphous carbon, orpoly-silicon. As an example, Atomic Layer Deposition (ALD), ChemicalVapor Deposition (CVD), or furnace oxidation may be used to form theprotection layer. Then, the photomask layer is patterned to expose thenitride barrier layer 301 on the second region 221 and the first oxidelayer 203 on the second region 221, the exposed nitride barrier layer301 on the second region 221 and the first oxide layer 203 are thenremoved. The remaining photomask layer may also be removed afterwards.Alternately, the photoresist of the remaining photomask layer is removedwhile the protection layer of the remaining photomask layer is retained.

In step 108, an oxidation process is conducted to form a second oxidelayer 501 on the second region 221, as shown in FIG. 5. The second oxidelayer 501 is for a Low Voltage device, and the thickness of the secondoxide layer 501 is less than the thickness of the third oxide layer 204.

This concludes the description of a semiconductor device manufacturingmethod in accordance with one or more embodiments of this inventiveconcept. In this manufacturing method, a nitride barrier layer is formedon the first oxide layer on the first region. During the oxidationprocess on the second oxide layer on the second region, the nitridebarrier layer prevents oxygen from contacting the first oxide layer onthe first region, and thus prevents the first oxide layer on the firstregion from being incidentally thickened by the oxidation process toaffect the threshold voltage of the device (such as a flash memory)formed in this region.

It is understood that although the first oxide layer in this inventiveconcept is a tunnel oxide layer for a flash memory device, it is notlimited herein. The manufacturing method of this inventive concept canapply to not only a flash memory device, but also other devices thatsuffer similar manufacturing problems.

After these processes, a flash memory may be manufactured on theresulting structure by existing processes. For example, a floating gateand a control gate may be formed on the nitride barrier layer on thefirst region, a Low Voltage device may be formed on the second oxidelayer on the second region, and a High Voltage device may be formed onthe third oxide layer on the third region. The Low Voltage device andthe High Voltage device can both be a logic device. Manufacturingprocess afterwards is not within the scope of this inventive concept,and therefore is omitted for conciseness.

This inventive concept further presents a semiconductor device.Referring to FIG. 5, this semiconductor device comprises a semiconductorsubstrate 201, which comprises a first region 211 and a second region221 that are mutually exclusive from one another. The first region 211and the second region 221 may be partially separated by a separationstructure 202 between them, which can be a Shallow Trench Isolation(STI) structure.

The semiconductor device may further comprise a first oxide layer 203 onthe first region 211 and a nitride barrier layer 301 on the first oxidelayer 203, the nitride barrier layer 301 may be made of siliconoxynitride (SiON). Optimally, the thickness of the nitride barrier layer301 may be from 3 Angstrom to 50 Angstrom. For example, it can be 10Angstrom, 30 Angstrom, or 40 Angstrom. In one embodiment, the firstoxide layer 203 is a tunnel oxide layer for a flash memory device. Thesemiconductor device may further comprise a second oxide layer 501 onthe second region 221.

Referring to FIG. 5, in one embodiment, the semiconductor device mayfurther comprise a third region 231 different from the first region 211and the second region 221. In this embodiment, the semiconductor devicemay further comprise a third oxide layer 204 on the third region 231,and the nitride barrier layer 301 may also cover the third oxide layer204. The thickness of the third oxide layer 204 is larger than thethickness of the second oxide layer 501.

In one embodiment, the semiconductor device may further comprise aprotection layer (not shown in FIG. 5) on the nitride barrier layer 301to prevent photoresist poisoning, the protection layer may be made ofsilicon oxide, amorphous carbon, or poly-silicon.

In another embodiment, the semiconductor device may further comprise afloating gate and a control gate (not shown in FIG. 5) on the nitridebarrier layer 301 on the first region 211.

This concludes the description of a semiconductor device and itsmanufacturing method in accordance with one or more embodiments of thisinventive concept. While this inventive concept has been described interms of several embodiments, there are alterations, permutations, andequivalents, which fall within the scope of this disclosure. It shallalso be noted that there are alternative ways of implementing themethods and apparatuses of the inventive concept. Furthermore,embodiments may find utility in other applications. It is thereforeintended that the claims be interpreted as including all suchalterations, permutations, and equivalents. The abstract section isprovided herein for convenience and, due to word count limitation, isaccordingly written for reading convenience and shall not be employed tolimit the scope of the claims.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor substrate comprising a first region and a second regionthat are mutually exclusive from one another; a first oxide layer on thefirst region; a nitride barrier layer on the first oxide layer; and asecond oxide layer on the second region.
 2. The device of claim 1,wherein the semiconductor substrate further comprises: a third regionthat is different from the first region and the second region, andwherein the device of claim 1 further comprises: a third oxide layer onthe third region, wherein the nitride barrier layer covers the thirdoxide layer, and the thickness of the third oxide layer is larger thanthe thickness of the second oxide layer.
 3. The device of claim 1,further comprises: a protection layer on the nitride barrier layer toprevent photoresist poisoning.
 4. The device of claim 3, wherein theprotection layer is made of silicon oxide, amorphous carbon, orpoly-silicon.
 5. The device of claim 1, wherein the nitride barrierlayer is made of silicon oxynitride (SiON).
 6. The device of claim 1,wherein the thickness of the nitride barrier layer is from 3 Angstrom to50 Angstrom.
 7. The device of claim 1, wherein the first oxide layer isa tunnel oxide layer for a flash memory device.
 8. The device of claim1, further comprising: a floating gate and a control gate on the nitridebarrier layer.